1. Field of the Invention
The invention relates to a lithographic apparatus, a device manufacturing method and a positioning system.
2. Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam of radiation in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Conventional lithographic apparatus generally include positioning systems that are configured to position one or more elements of the apparatus. These elements can be, for example, a (part of an) illumination system, a (part of a) support structure, a (part of a) substrate table or any other suitable constituting element of the lithographic apparatus. The positioning systems frequently include a plurality of actuators, e.g. separate actuators for different directions, however it is also possible that two or more actuators are applied for a same direction, e.g. an actuator for a course, long stroke positioning and an actuator for a fine, short stroke positioning. Also, one or more of the actuators can function as a gravity compensation to compensate forces acting on parts of the lithographic apparatus due to gravity.
Frequently, the actuators make use of a magnetic actuator, such as linear motor, a magnetic gravity compensator, a motor (e.g. a voice oil or Lorentz actuator) etc.
However, a field generated by one of the actuators, such as a magnetic or electromagnetic field, may act on another one of the actuators, the actuators thus influencing each other. The field generated by the one of the actuators in its operative condition may result in a force acting on the other one of the actuators, and thus in a disturbance or error of the other one of the actuators.